1. Field of the Invention
The present invention relates to a secondary battery negative electrode material, a secondary battery negative electrode, a method for manufacturing a secondary battery negative electrode material, and a method for manufacturing a secondary battery negative electrode, and more particularly, it relates to a secondary battery negative electrode material constituting an active material layer and a method for manufacturing the same, and a secondary battery negative, electrode including an active material layer and a method for manufacturing the same.
2. Description of the Background Art
In recent years, Si having a large charge-discharge capacity has been regarded as a promising active material (secondary battery negative electrode material) of a secondary battery negative electrode, in order to increase the capacity of a lithium ion secondary battery. However, Si is known to significantly decrease the discharge capacity of the secondary battery negative electrode from an initial value (decrease the charge-discharge cycle, life) when the lithium ion secondary battery is repeatedly charged and discharged. The reason why Si decreases the charge-discharge cycle life is considered to be because the secondary battery negative electrode is disrupted by stress generated in the secondary battery negative electrode due to a difference between the volume of the secondary battery negative electrode during charging and the volume of the secondary battery negative electrode during discharging and partially becomes non-functional.
As one way to suppress decrease in the charge-discharge cycle life, it is proposed to employ an active material having Si particles whose surfaces are Ni-plated as an active material of a lithium ion secondary battery negative electrode. Such an active material including Si particles whose surfaces are Ni-plated is disclosed in Japanese Patent Laying-Open No. 2005-63767, for example.
In Japanese Patent Laying-Open No. 2005-63767, there are disclosed active material particles (secondary battery negative electrode material) constituting an active material layer of a secondary battery negative electrode and including Si particles and metal thin films of Ni plating formed to cover surfaces of the Si particles. In this manner, Ni plating is performed to cover the surfaces of the Si particles, whereby the Si particles can withstand stress generated in the secondary battery negative electrode, and disruption of the Si particles can be suppressed. Thus, decrease in the charge-discharge cycle life can be suppressed.
However, although the active material particles including the Ni-plated Si particles described in Japanese Patent Laving-Open No. 2005-63767 can be employed to increase the charge-discharge cycle life and improve, the charge-discharge capacity of the secondary battery negative electrode to some extent, in recent years, it has been desired to further improve the charge-discharge capacity while increasing the charge-discharge cycle life.